Tubular electrostrictive transducer with spaced electrodes and loading masses



Dec. 11, 1962 s. L. EHRLICH ET AL 3,068,445

TUBULAR ELECTRQSTRICTIVE TRANSDUCER WITH SPACED ELECTRODES AND LOADING MASSES 2 Sheets-Sheet 1 Filed Aug. 21, 1958 QEDQ REWQINQ RENQWQ Dec. 11, 1962 s. EHRLICH ET AL 3,068,446 TUBULAR ELECTROSTRICTIVE TRANSDUCER WITH SPACED ELECTRODES AND LOADING MASSES Filed Aug. 21, 1958 2 Sheets-Sheet 2 CEMENT BONDS INVENTORS. JZ M LfY A 54/?4/0/ 44670? 54 roe 0K Filed Aug. 21, 1958, Ser. No. 756,492 6 Claims. ((31. Mil-$) (Granted under Title 55, US. {lode (15*52), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the pa ment of any royalties thereon or therefor.

This invention relates to transducers, and particularly those applicable for underwater telephone systems. It has especial application as part of the underwater telephone equipment that is carried by underwater swimmers.

In recent years, underwater activities of free swimmers who carry their breathing supplies with them in the water have expanded greatly in scope and range. Hence, provision of equipment by which such swimmers during their activities can communicate with one another or with a base station has become of great importance.

An object of this invention is to provide a transducer for underwater use as part of a communication system, which will be directional in operation, adequately sensitive, unafiected physically by the water in which it may be submerged, which will be of such compactness, size and shape that it can, when desired, be conveniently held in a swimmers hand or secured to the person of a swimmer, which has minimum possible weight so as to lighten the equipment a swimmer must carry and which is relatively simple, practical, effective, sensitive, durable, compact and inexpensive.

Other objects and advantages will be apparent from the following description of two examples of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

in the accompanying drawings:

FIG. 1 is an end elevation of a transducer made in accordance with this invention;

FIG. 2 is a longitudinal, sectional elevation of the same, the section being taken approximately along the line 22 of FIG. 1;

FIG. 3 is a view similar to FIG. 2, of one end part of the transducer, and illustrating a slight modification thereof;

FIG. 4 is a transverse, crosssectional view of a cylinder of electrostrictive material having thereon a different arrangement of conducting surfaces or electrodes that may be employed in the transducer;

PEG. 5 is a view similar to FIG. 4 but illustrating another arrangement of electrodes or conducting surfaces; and

FIG. 6 is a side elevation of a portion of a cylinder of electrostrictive material having thereon still another arrangement of conducting surfaces.

In the example of the invention illustrated in FIGS. 1 and 2, the transducer employs an elongated member 16 of electrostrictive material having faces or surfaces of substantial areas that extend longitudinally thereof and which are uniformly spaced apart and carry adherent thin, film-like coatings of a suitable metal. In the illustrated example, this member 10 is of tubular shape, such as a circular, hollow cylinder having adherent, film-like, sliver coatings on its inner and outer peripheral surfaces, with the thickness of the wall of the cylinder approximately uniform. While any electrostrictive material for this member or cylinder it may be employed, an axially 33,58,446 Patented Dec. 11, 1952 elongated cylinder of barium titanate with thin, adherent, metallic silver coatings on its inner and outer peripheral surfaces is especially advantageous for this purpose, and the member 10- employed should have a longitudinal mode of vibration. The cylinder with electroded surfaces is polarized in the usual manner for electrostrictive transducers.

A loading mass 11, relatively heavy, such as of metal, for example of brass, has one end face abutting against and secured to one end of the member or cylinder 10. On its end face secured, such as by cement, for example, to cylinder 1%, it has an annular shoulder 12 with which th cylinder 16 telescopes slightly, so as to keep the mass 11 centralized over the end of the cylinder that it abuts. An energy propagating and receiving element 13, such as of aluminum or light metal alloy, is disposed with a face abutting and secured such as by cement, for exam pie, to the opposite end face of the member or cylinder 1%. The face of this element 13 which is secured to the end of member 10 is also provided with an annular shoul der 14 which telescopes slightly with the adjacent end of member 11} to keep the element 13 centralized over the end of the member 10. The opposite end face 15 of element 13 is substantially larger than the end face that is attached to the member 10, in order to present a substantial, large, face area to the water for imparting substantial vibrations to the water and for having adequate response to vibrations in the water that impinge thereon. The large exposed face area of element 13 can create vibrations in the water of adequate energy, and will be responsive and sensitive to vibrations in the water impinging thereon. A simple way of providing this relatively large exposed face area 15 on element 13 is by making the element frusto-conical in shape, and securing its smaller end face to the member 10.

A layer of sheet material 16 of a material which acts as a shield against mechanical and other vibrations, such as a mixture of a live rubber-like material and cork, is provided entirely around the cylinder 10 for its full length, and a similar layer 16a of the same or similar material snugly surrounds and covers this layer 16, the periphery and exposed end of the loading mass 11, and the periphery of the frusto-conical element 13. The material of layers 16 and 16a may, for example, be a mixture of a live rubber-like material such as neoprene and finely divided particles of cork. Such a product is available in the market under the name of Corprene. This leaves only the face 15 of element 13 fully exposed to vibrations and to protect this exposed face 15 from corrosion, it may be, and preferably is, covered by a disc 18 of a material which is transparent to mechanical vibration energy. This disc is bonded to the face 15 in a manner to preclude air spaces or cells therebetween, such as, for example, by cyclewelding. Such a disc may be made of neoprene.

An electric cable 19 having two wires 24) therein enters the chamber in cylinder 10 through the loading mass and the layer 16a of shielding material, and within the cylinder one of the wires 29 is attached to the silver or other conducting coating on the exterior peripheral surface of member Ill, and the other wire Zll is attached to the conducting coating on the inner peripheral surface of the cylinder. An end of the cylinder or member 111 may be notched to pass the wire which is attached to the coating on the exterior of the member 1%). A moisture impervious boot 21 snugly encases the layer 16a, overlies slightly the peripheral margin of disc 18, and extends a short distance along the cable 19 away from the loading mass. This boot may be made of live rubber or rubber substitutes or equivalents, and live neoprene is an example of a rubber substitute or equivalent that may be used. The end faces of mass 11 and element 13 which abut the 3 cylinder ends are somewhat reater in diameter than the diameters of the ends of the cylinder, by an amount to provide for the extra layer 16 of vibration shielding material.

In the example illustrated in 'FIG. 3, the construction is similar to that shown in FIGS. 1 and 2, except that a boss 22 is provided on the cable to abut against the inside face of the loading mass 11, and the wires 2% are connected to the conducting coatings on the inside and outside peripheries of the cylinder at the end adjacent the loading mass 11.

In use as a sending device when potential differences are applied by wires of cable 19 to opposite, spaced faces of the member 18 of electrostrictive material, the member 10 changes its length proportionally to the applied potential diiferences. When member 10 changes its length in response to changes in potential applied thereto, its one end is held against substantial movement by the loading mass 11 and its other end which carries the lighter element 13 will then vibrate with a frequency and amplitude proportional to the frequency and intensity of the said potential changes. Since element 13 has a planar face exposed to water, its vibration in the water will propagate in the water desired vibrations corresponding to the variations in said potential diiferences'to which the member It) is subjected. This transducer thus acts to send through or propagate in the water vibrations corresponding to the potential differences on the member It When the transducer is used as a receiver, the vibrations in the water impinging against the exposed planar end face of element 13 and disc 18, will cause the element 13 to compress the cylinder or member to varying degrees against loading mass 11, and this stress on the member 10 of electrostrictive material will create changes in the electric potentials on the metallic coatings on the cylinder or member 10 which can be conducted away by wires 21) as signals corresponding in frequency and amplitude to the frequency and amplitude of the waterborne vibrations that impinge on element 13. 1

The mass 11 being heavier than element 13 is an inertia mass and will resist endwise forces on the cylinder 10 and hence vibratory forces acting on element 113 will stress the cylinder 10. Similarly, when cylinder 10 is stressed by potential changes on its inner and outer peripheries, it will expand endwise, and since mass 11 resists movement in one direction, the expansion will be effective on the lighter element 13. The layers in; and 16a prevent stresses on the cylinder 10 from vibrations that reach cylinder 10 of the transducer from directions sidewise thereof, and the loading mass 11 minimizes stresses from that end direction upon the cylinder lit Hence, the transducer is highly directional and will be responsive mainly'to vibrations received in an endwise direction on the exposed face 15 of element 13.

The transducer has outside dimensions which approximate those of an ordinary 2-cell flashlight, so that one can hold it in ones hand and by turning it in different directions send or receive signals only in selected directions. The wires 26 are preferably attached to the end of the cylinder or member 19 to which the loading mass 11 is attached where the motion of the cylinder is a minimum. In this way the inertia and resistance to flexing of the wires will have a minimum of influence on the action of propagating and receiving element 13.

In the example of the invention illustrated in FIGS. 1-3, where the cylinder of electrostrictive material is provided on its inner and outer peripheral surfaces with the conducting layers that may be approximately coexten- 'sive with those surfaces, the polarization of such material is radially of the cylinder, and the polarizing voltage is applied across the conducting layers on the inner and outer peripheries of the cylinder. In FIG. 4, the conducting electrodes or layers on the inside and outside peripheries of cylinder 24 are in the form of strips 25, and 26 that extend longitudinally 6r lengthwise of the cylinder, the strips 25 being parallel to one another and arranged in a peripherally spaced apart relation on the inside surface of the cylinder, and the strips 26, also parallel to one another, being equal in number to strips 25 and arranged in a similar peripherally spaced-apart relation on the exterior periphery of the cylinder, but in circumferentially spaced or offset relation to the strips 25. The strips 2-5 and 26 are thus arranged in pairs with the strips of each pair circumferentially oflfset somewhat out of alignment with one another, as shown in FIG. 4. The polarizing voltage will be applied to the strips of each pair. Because of this staggered or circumferentially offset arrangement of the conducting strips 25 and 26 of each pair, the vibrations of the cylinder, due to polarization, are partly radial and partly circumferential when signal voltages are applied to the strips of each pair. These circumferential and radial vibrations cause the cylinder to expand and contract in diameter. Since the volume of material in the cylinder is constant, an increase in the diameter of the cylinder will automatically cause it to contract lengthwise, and a decrease in its diameter will cause the cylinder to increase in length. In other words, this circumferential polarization couples into the longitudinal mode.

In FIG. 5, the cylinder 27 is formed of a plurality of longitudinally extending cylinder segments 28 adhesively or cement-itiously secured together edge to edge to complete the cylinder, but with a layer of conducting material or metallic strip 29 between each two abutting segment surfaces or segments that are adhesively or cementitiously connected together. In this form, the action is similar to that of the cylinder of FIG. 4 in that the polarization is circumferential, except that vibrations of the cylinder are primarily circumferential when signal voltages are applied across adjacent strips 29, and are coupled into the longitudinal mode for the same reasons given for the cylinder of FIG. 4.

In FIG. 6, the cylinder 3d has on one of its peripheral surfaces, such as the outer peripheral surface, for example, a plurality of circumferentiallyextending strips or hands 31 of conducting material that are adherent to the cylinder and spaced apart in a direction lengthwise of the cylinder. The strips 31 are preferably circumferentially continuous for ease of manufacture. Since the polarizing voltages are applied to the parts of circumferentially extending strips, the polarization will .be in directions parallel to the axis of the cylinder. In this form, the vibrations of the cylinder due to polarization are primarily lengthwise of the cylinder and one achieves the highest electromechanical coupling coefficient with this mode of polarization.

In all of the illustrated embodiments of the invention, the cylinder and segments are made of any suitable electrostrictive material, of which barium titanate is one excellent example, and the conducting layers, strips or electrodes on the electrostrictive material may be of any suitable adherent metal, such as metallic silver coatings, for example.

This application is a continuation-in-part of copending application Serial No. 651,767, filed April 9, 1957.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

We claim:

1. An electrostrictive transducer which comprises a piezoelectric ceramic hollow cylinder that is active in the longitudinal mode and has electroded inner and outer cylindrical surfaces, a circular cylindrical loading mass seating against one end of said cylinder coaxially therewith, the diameter of said loading mass being somewhat larger than the diameter of said cylinder, a frustoconical loading mass lighter than said cylindrical loading mass, the smaller diameter end of frusto-conical loading mass being substantially equal to the diameter of said cylindrical loading mass and seating against the other end of said cylinder, vibration energy inhibiting means overlaid on the circular surface and free end surface of said cylindrical loading mass, on the outer surface of said cylinder, and on the conical surface of said frusto-conical loading mass, electrical conductor means connected to the electroded inner and outer peripheries of said cylinder and extending beyond said circular loading mass, 2. layer of rubber-lile material bonded free of air spaces to the larger diameter surface of said frusto-conical loading mass, and a rubber-like boot encasing said transducer between the rim of said layer of rubber-like material and the opposite end thereof.

2. An electrostrictive transducer comprising a piezoelectric ceramic cylinder that is active in the longitudinal mode and has electroded coatings spaced apart in directions lengthwise of the cylinder, a loading mass seating against one end of said cylinder, a frusto-conical loading mass lighter in Weight than the preceding mass, the smaller diameter end of said frusto-conical loading mass being somewhat larger than the diameter of said cylinder and seating against the other end of said cylinder, vibration energy inhibiting means overlaid on the lateral surface and free end surface of said firstmentioned loading mass, on the outer surface of said cylinder, and on the conical surface of said frusto-conical loading mass, electrical conductor means connected to said electroded coatings of said cylinder and extending past said first mentioned loading mass, a layer of elastic rubber-like material bonded free of air spaces to the larger diameter surface of said frusto-conical loading mass, and a rubber-like boot encasing said transducer between the rim of said layer of rubber-like material and the opposite end thereof, leaving said layer of elastic material exposed for contact with the vibration transmitting fluid medium through which vibrations are sent and received.

3. An electrostrictive transducer which comprises an elongated body of electrostrictive material having on its exterior surface a plurality of transversely encircling electrically conducting, adherent, exposed layers spaced apart in the direction of such elongation, a loading mass provided on one end part of said body, an energy propagating and receiving element provided on the other end part of said body and having an exposed planar end face, a layer of a material resistant to the transmission of vibration energy therethrough covering the exposed outer surfaces of said body, said loading mass and the periphery only of said energy propagating and receiving element, leaving said planar end face uncovered and exposed to the fluid medium through which vibrations to and from said planar end face are transmitted, electrical conductors connected to spaced conducting layers and having ends available for connection in an electric circuit, and a water impervious envelope surrounding the part of the transducer which is covered by said layer of material and limiting contact of water with said trans ducer solely to said planar end face.

4. The transducer as set forth in claim 3, wherein said exposed planar end face of said element is of substantially larger overall dimensions than its opposite end face.

5. The transducer as set forth in claim 3, wherein said energy propagating and receiving element is frusto-conical with its larger end face as the exposed planar end face.

6. An eleotrostrictive transducer which comprises a piezoelectric, open ended tubular element that is active in the longitudinal mode and has electroded inner and outer surfaces, a loading mass seated against and secured to one end of said element coaxially therewith, a vibration propagating body lighter in Weight than said loading mass abutting endwise against and secured to the other end of said element and having a free planar end face, vibration energy inhibiting means overlaid on the lateral surface and free end surface of said loading mass, on the outer surface of said element, and on the transversely peripheral surface of said propagating body, leaving said planar end face of said body uncovered by said energy inhibiting means, electrical conductors connected to said electroded surfaces of said element and having ends available for connection in an electric circuit, and a water impervious boot surrounding the part of the transducer which is cove-red by said vibration energy inhibiting means, said transducer having a diameter of a size which may be firmly grasped by an adult persons hand.

References Cited in the file of this patent UNITED STATES PATENTS 2,076,330 Wood et a1. Apr. 6, 1937 2,374,637 Hayes Apr. 24, 1945 2,430,013. Hansell Nov. 4, 1947 2,430,535 Alois et al Aug. 30, 1949 2,605,346 Gogolick et al. July 29, 1952 2,616,223 Jonker Nov. 4, 1952 2,684,726 Ebaugh et a1. July 27, 1954 2,787,777 Camp Apr. 2, 1957 2,800,647 Baerwald et al July 23, 1957 2,880,404 Harris Mar. 31, 1959 2,961,637 Camp Nov. 22, 1960 2,962,695 Harris Nov. 29, 1960 FOREIGN PATENTS 815,873 Great Britain July 1, 1959 OTHER REFERENCES MIL-C-17831A (Ships) February 16, 1956, 23 pages. 

